It's early morning and you see some mayflies floating
down the stream. Where will your chances for success
be best? It's mid morning and caddisflies are hopping
off the water in clouds. What is the best approach to
this situation? It's late afternoon and caddisflies are
returning to the water to lay their eggs. What can you
do to maximize your chances for success?

Those are common questions I get asked in one form or
another all summer long. The new guy is using the right
fly, he's on the right stream, he's wearing the right
clothes, but he can't buy a strike. The guy a few
hundred feet upstream is catching one fish after another
while this poor soul is doomed to watch the show and go
fish-less for his efforts. Why does that happen?

I think we can find an answer in the habits of insects
and the fish that eat them. Certain insects act in
certain ways, and the fish react to those insects in
predictable ways. If you understand the insects and
how fish react to them, you can profit from that
understanding with more fish on the end of your line.
Let's look at the four major groups of aquatic insects,
how they hatch, how they lay their eggs, and how the fish
react to them; and then see if it helps us understand
better how to use that information to our advantage.

Mayflies

Mayflies, like all aquatic insects, have a bunch of
sub-families and each family has a few differences in
how they act. However, there are a few generalizations
that can be helpful in our quest for fish. When mayfly
nymphs reach the level of maturity to move to the surface
to morph into their first stage of adulthood, many of
those nymphs make that move by swimming to the surface.
This movement puts the nymphs in harm's way as they
travel through the dining area of the fish. Fortunately,
the nymphs have a trick or two to minimize the threat.

Mayflies in moving water tend to migrate to faster and
shallower water to make their move to the surface. This
results in a shorter trip and less surface tension they
have to deal with. The unlucky nymphs who happen to make
the trip in deeper water with a calm surface (lakes and
deep pools in moving water) find the trip more perilous
and the surface tension much harder to break. As a result,
the sub-species that hatch in slower water are usually
better swimmers. They also tend to have more stillborn
casualties (flies that didn't succeed in busting the
surface tension) than mayflies who emerge in fast water.

Fish react to these differences in different ways. When
a hatch is getting ready to start, fish in moving water
start seeing nymphs drifting in the water after they were
dislodged while moving into fast and shallow water to
prepare for emergence. The fish move up into that thin
water to feed on the nymphs that are drifting near the
bottom. As the hatch starts, the focus of the fish shifts
to looking for movement toward the surface. Then, as
more adults emerge and ride the surface of the water,
fish start looking for adults on the surface to feed on.
In most cases, the feeding habits overlap as the hatch
progresses.

In calm water, mayfly nymphs are usually swimming sub-species
designed to travel the longer distances from the bottom of
the water to the top. Fish first key in on a hatch by
noticing the swimming ascent to the surface being made
by growing numbers of nymphs. In this case, motion is
a key factor in fish feeding behavior. Movement upward
and jerky movements just under the surface signal to
the fish that insects are ascending to the surface and
trying to break through the surface. As more insects
are successful in this migration, fish eventually turn
more attention to the mayflies riding the surface, but
for the most part, the fish are more attuned to the
jerky movements just under the surface.

When a hatch is just starting in moving water, a dead-drifted
beadhead or weighted nymph of the right size and color can
be your best bet if you concentrate your fishing on the
faster and shallow water of the riffles and rapids. As
the hatch progresses, an upward lift applied to the nymph
can often result in more strikes. When significant numbers
of adults can be seen on the surface, match the insect
with a dry fly and concentrate your efforts on the areas
where the riffles lead into pools. The majority of the
fish will be in these areas feeding on insects that are
acting this way.

After mayflies mate, they return to the water upstream
from where they emerged and lay their eggs in pools of
calm water. The eggs drift to the bottom to restart
the cycle and the adults die on the water's surface.
Fish will be feeding near the bottoms of those pools
or anywhere the water swirls to concentrate the dead
adult mayflies. In lakes, fish will swim under the
surface and pick off dead mayflies at random but somewhat
predictable intervals. In both cases, flies should be
presented by dead-drifting them on the surface.

Caddisflies

Caddisflies share some habits with mayflies, but they
are also very different. Caddisflies prefer to emerge
in shallow, moving water like mayflies, but they do so
much faster than mayflies. Their pupae are also better
swimmers than mayfly nymphs. Unlike mayflies who often
drift for up to an hour while their wings dry, caddisflies
are often airborne within seconds of their emergence on
the water's surface. Before the hatch occurs, caddisfly
larvae pupate, so you don't see a concentration of
caddisfly larvae near the bottom just before the hatch.

Fish key in on the hatch by looking for rising and
swimming pupae as the hatch starts. Since the adults
spend so little time on the surface before they fly away,
adult patterns are less important than wet flies that
imitate the emerging pupae. Fish in lakes look for
the rising pupae and the jerky motion of pupae just
under the surface trying to break through the surface
tension to emerge as adults.

Most adult caddisflies lay their eggs by flying upstream
while skimming the water's surface and dipping their tail
to deposit their eggs, or landing briefly to deposit some
eggs then flying upstream to another location to repeat
the land and go process again many times. Egg laying
is often done in the riffles just above pools or at
the head of pools. After the eggs are laid, the adults
often fly off to die on land instead of on the water
like adult mayflies.

The best approach to fishing caddis hatches is to concentrate
on riffles with a wet fly that imitates a rising caddis pupa,
fishing a surface emerger like a sparkle pupa with a slight
twitch, or fishing a sparsely tied adult with a jerky of
fluttering twitch. To imitate an egg laying adult,
skitter an bushy fly like and elk hair caddis on the
surface with an upstream movement. Especially effective
is a stop and go skitter that allows the dry fly to pause
for a fraction of a second before it moves upstream again.
Motion of your fly is important in both the emergence and
egg laying stages of the life cycle.

Midges

Midges are very similar to caddisflies in many ways.
However, they seem to prefer calmer water to emerge in,
spend more time working through the surface tension,
and often return to the water to lay their eggs in
mating clusters. Larvae imitations usually fish best
in the heads of pools and along seams in slow moving
water. Emerger patterns usually fish best in the
calm water near the head of a pool, fished with a
short twitch to imitate insects trying to break
through the surface tension. Cluster type flies
like the Griffith's gnat are effective egg laying
adult imitations and fish best on a dead-drift with
random short twitches. Lake fishing is similar to
caddisfly fishing except any movement should be
slower and in much shorter increments.

Stoneflies

Stonefly nymphs usually crawl out of the water to emerge
as adults on rocks or weeds near the edge of the stream.
As a result, they are usually available to the fish only
as dislodged nymphs or egg laying adults.

As the hatch nears, nymphs move along the bottom of
the stream to the water's edge where they crawl out.
Many of them become dislodged and are available to
the fish near the bottom of the stream, especially
near the edges of the stream. Imitations fish best
when dead-drifted near the bottom and near the
stream's edge. Adults usually lay their eggs by
dipping their tails into the water as they zigzag
upstream in flight. Bushy patterns like the
stimulator that are skittered in a zigzag motion
upstream are often most effective. Eggs are
usually laid in the bottoms of riffles or the
tops of pools. Adults usually die on land, so
dead-drifted adult patterns aren't usually as
effective.

We didn't cover dragonflies and damselflies, but those
are best left to another article. At best, this is a
simplified version of how the insects act and how the
fish react to them. However, if you pay attention to
the stages of the hatch and fish accordingly, your
catch rates should improve a lot. ~ AC